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JEE Advanced levelSingle correct optionDifficulty 3 of 3cc075

$[Co (NH X_{3}) X_{6}] [Cr (CN) X_{6}]$ is a coordination isomer of $[Cr (NH X_{3}) X_{6}] [Co (CN) X_{6}]$ . The IUPAC name of the first compound is

Ahexaamminecobalt(II) hexacyanidochromate(III)
Bhexaamminecobalt(III) hexacyanidochromate(III)
Chexacyanidochromate(III) hexaamminecobalt(III)
Dhexaamminecobalt(III) hexacyanidochromate(II)

Answer: B

The cation is

[Co (NH X_{3}) X_{6}] X^{n +}

and the anion is

[Cr (CN) X_{6}] X^{n -}

, and the two charges must cancel. NH3 is neutral, so

n

is the oxidation state of Co. For the anion

x - 6 = - n

gives Cr =

6 - n

. Equal charges with

n = 3

give Co(III) and Cr(III) (the common state of both). The cation is named first and the anion ends in -ate.

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